1 Magnetohydrodynamics.- 2 Decay and Amplification of Magnetic Fields.- 3 Dynamo Models of the Solar Cycle.- 4 Fluctuations, Intermittency and Predictivity.- 5 Stellar Dynamos.- A Useful Identities and Theorems from Vector Calculus.- B Coordinate Systems and the Fluid Equations.- C Physical and Astronomical Constants.- D Maxwell's Equations and Physical Units.- Index.